It seems like a meta tag to me:
If the tag can’t work as the only tag on a question, it’s probably a meta-tag.
I don't think typo would ever work as a tag on its own. No one would ever want to look through the list of typo questions (presumably all closed), nor would anyone want to follow questions tagged typo. What's more, new questions would never be tagged this way because no one would ask a typo question on purpose, and seeing "typo - Did the author forget to use 'if' or I'm missing some literary style" on Google would just be strange.
(We had this problem on Japanese.SE and ended up burninating the tag.)
I don't think we should add typo to questions on ELL.